Electrical contacts containing gettering material

ABSTRACT

An electrical contact for a vacuum interrupter consists of a binary alloy of 95 to 99 percent tungsten and 1 to 5 percent tantalum, which alloy when heated during contact arcing getters undesirable hydrogen which may be present in the interrupter.

United States Patent [72] Inventor Henry J. Wesoloski Milton, Mass. 211Appl. No. 772,347 [22] Filed Oct. 31, 1968 [45] Patented June 29, 1971[73] Assignee Allis-Chalmers Manufacturing Company Milwaukee, Wis.

[54] ELECTRICAL CONTACTS CONTAINING GETTERING MATERIAL 2 Claims, 1Drawing Fig.

[52] 11.8. C1 200/166 C, 200/144 B, 75/174, 75/176 [51] lnt.Cl 1101b1/02, H0111 33/66 [50] Field otSearch 200/1442, 166C; 75/174, 176;252/1816; 219/145, 146

[56] References Cited UNITED STATES PATENTS 2,321,910 6/1943 Hays252/1816 X 2,785,285 3/1957 Bernard... 219/146 3,198,932 8/1965Weatherly 219/145 3,270,172 8/1966 Chubb 200/144 (.2) 3,379,846 4/1968Wood et a1. 200/144 (.2) FOREIGN PATENTS 693,827 9/1964 Canada 200/144(.2)

1,201,164 12/1959 France 200/166 (C) 211,693 2/1968 U.S.S.R. 200/166 (C)OTHER REFERENCES TUNGSTEN AND ITS COMPOUNDS, by G. D. Rieck, copyright1967 by Pergamon Press; p. 77; copy in scientific library of patentoffice. I

THE METAL TANTALUM, by Fansteel Metallurgical Corp., copyright 1951; p.16; copy in Or. 110; class 75/174 Primary Examiner-Robert K. SchaeferAssistant ExaminerRobert A. Vanderhye Attorneys-Thomas F. Kirby, RobertB. Benson and Lee H.

Kaiser ABSTRACT: An electrical contact for a vacuum interrupter consistsofa binary alloy of 95 to 99 percent tungsten and 1 to 5 percenttantalum, which alloy when heated during contact arcing gettersundesirable hydrogen which may be present in the interrupter.

SUMMARY OF THE INVENTION This invention relates generally to electricalcontacts and particularly to contacts containing gettering material usedin vacuum switches or similar interrupting devices hereinafter referredto as vacuum switches.

One type of vacuum switch comprises an evacuated envelope in whichrelatively movable tungsten contacts are enclosed. In normal operation,arcing which occurs upon contact separation is quickly extinguished.However, if impurities in the form of undesirable gases are presentinside the envelope, then arcing is not readily extinguished and a riskof flashover between the contacts exists, particularly if alternatingcurrent is involved. One gaseous impurity often present is hydrogenwhich may evolve from several sources. For example, a monolayer of wateron the surface of components or entrapped in component materials,particularly those which have been hydrogen fired or brazed duringmanufacture and assembly, may serve as a source of hydrogen. Steps toreduce the presence of undesirable hydrogen, such as bakeout and qualitycontrol in material selection, are not always completely successful.Furthermore, the high temperatures which exist inside the envelopeduring arcing causes evolution of hydrogen which may not have beencompletely released during manufacture and processing.

It is known that gettering materials can be employed inside theevacuated envelope of vacuum interrupters to getter hydrogen. However,such materials heretofore have been arranged as a separate component oras a surface plating on some other component. It is desirable, however,to provide improved gettering means.

In accordance with the present invention, a hydrogen-gettering materialsuch as titanium or tantalum is alloyed with the tungsten material ofwhich the contacts are made. Preferably, the alloy consists of 95 to 99percent tungsten and 1 to 5 percent tantalum. During contact arcing whenheating causes evolution of hydrogen, the gettering material is alsoheated and its gettering efficiency greatly increased.

OBJECTS It is an object of the present invention to provide improvedgettering means for vacuum switches.

Another object is to provide such gettering means which are disposed atan optimum location within the vacuum switch.

Another object is to provide improved gettering means of the aforesaidcharacter in which the gettering material selected has increasedaffinity for gettering hydrogen at elevated temperatures and is locatedat the position which is hottest.

Another object is to provide a gettering means of the aforesaidcharacter wherein the gettering material is alloyed with the contactmaterial.

Another object is to provide a tungsten vacuum switch contact whichcomprises tantalum as gettering materials.

Another object is to provide such a contact which comprises 95 to 99percent tungsten and l to 5 percent tantalum.

Other objects and advantages of the invention will hereinafter appear.

DRAWINGS In the drawing, there is shown a vacuum switch which employselectrical contacts in accordance with the present invention.

DESCRIPTION OF THE INVENTION Referring to the drawing, there is shown avacuum switch which comprises a bottle 1 made of insulating material andhaving metallic end plates 2 and 3 sealed thereto to define a chamber 4within which a stationary contact rod 5 and a movable contact rod 6 aredisposed. Rods 5 and 6 are preferably copper. A bellows 7 is secured toend plate 3 and contact rod 6 to permit axial movement of contact rod 6to contact open and contact closed positions. Contact rods 5 and 6 areprovided at their inner ends with contacts 8 and 9, respectively. Ashield 10 is disposed on contact rod 5. Chamber 4 is understood to beevacuated to a pressure of at least l0 mm. of mercury.

In accordance with the present invention, either or both of contacts 8and 9 are fabricated of an alloy consisting of tungsten and tantalum ortungsten and titanium. In a preferred embodiment, to 99 percent of thealloy is tungsten and l to 5 percent of the alloy is either titanium ortantalum. Alloys of tungsten-tantalum are commercially available, forexample, from the Metals Division of the National Research Corporation.Alloys of tungsten-titanium can be fabricated by melting titanium intosintered tungsten in a manner similar to that in which copper is meltedinto sintered tungsten. If preferred, a tungsten contact could be coatedwith tantalum powder and the contact material and tantalum powdersintered together to provide the alloy primarily at the contactsurfaces. On account of the high degassing temperature required fortantalum, tungsten is suitable as a base metal for tantalum powder. Thetantalum or titanium in the contacts acts as a getter when arcing occursas contacts 8 and 9 are separated while current is flowing therethrough.

As previously explained, hydrogen present in space 4 of the vacuumswitch evolves from various sources primarily during arcing when thevacuum switch components are raised to extremely high temperatures. Thepresence of hydrogen in undesirable amounts make for a gassy" vacuumswitch which tends to be unreliable.

Tantalum has an affinity for absorbing hydrogen very readily at thetemperatures to which the tungsten-tantalum alloy contacts 8 and 9 orportions thereof would be raised when arcing occurs in vacuum switch 1.Specifically, tantalum absorbs up to 55 times its volume at red heat andup to 700 times its own volume at yellow heat. Carefully degassedtantalum sheets may absorb hydrogen to the extent of 740 times itsvolume provided that the temperature does not exceed 800 C. Optimumabsorption occurs at about 600 C. In any event, the maximum gettering issecured by service wherein the contact or portions thereof operate atred to yellow heat.

It is to be noted that the vapor pressure of tantalum is almost equal tothat of tungsten, therefore, these materials are compatible at the hightemperatures to which they would be raised during arcing. Furthermore,tungsten has a melting point of 3,380 C, and tantalum has a meltingpoint of about 2,996 C. 50 C. Tantalum can be brazed to itself and toother metals such as copper and tungsten if the braze material containsnickel and if the process is carried out in a vacuum at a pressure nothigher than 10 torrs.

It is to be understood that titanium has properties similar to that oftantalum at least as regards the properties discussed herein whichenable tantalum to be employed as a suitable hydrogen getter in analloy.

The embodiments of the invention in which I claim an exclusive propertyor privilege are defined as follows:

1. An electrical contact consisting of a composition of tungsten andtantalum.

2. A contact according to claim 1 consisting of about 95 to 99 percenttungsten and about 1 to 5 percent tantalum.

1. An electrical contact consisting of a composition of tungsten andtantalum.
 2. A contact according to claim 1 consisting of about 95 to 99percent tungsten and about 1 to 5 percent tantalum.